1. Field of the Invention
The present invention relates generally to communications systems using modems, and more specifically, to signaling capable modems and telecommunication systems that promote compatibility in new and existing networking technologies.
2. Description of Related Art
With advancements in communications technology, multimedia and telecommunication services have become more prevalent in our industry. The emergence of multimedia in the marketplace, coupled with the adoption and increasing implementation of new networking technologies such as integrated services digital network (ISDN), frame relay (FR) network, broadband ISDN and the Internet has brought to the attention of network designers certain practical communication compatibility issues associated with the integration and coexistence of these new networks with the standard `telephony` network, also known as plain old telephone service (POTS) or public switched telephone network (PSTN). Furthermore, the advances in voiceband modem, or standard non-signaling modem, technology has made their capability suitable for many multimedia applications.
Modem technology also benefits when a universal service is available that has made its use ubiquitous and easy. The implementation of a universal service allows for the advancement of such technology at a faster rate. Therefore, there is a need for interworking between the new (e.g., ISDN, FR, the Internet) and the existing (e.g., voiceband modems, POTS) networking technologies.
One major compatibility issue relates to the diverse types of calls that a caller using multimedia terminal devices can initiate to a called party whose subscriber line characteristics and terminal device media support capabilities are unknown. For example, when a caller using an ISDN compliant multimedia service wants to communicate with a called party whose access line arrangement and terminal device media support capabilities are unknown, the caller can start a call based on the lowest common denominator capability and after the connection, establish the higher available capabilities, acquiring a higher capacity channel. Such requirements from the terminal devices can often be too demanding, since the terminals need to have a number of standard technological capabilities. This problem is exacerbated as the number of communication standards grows. On the other hand, if the call is initiated using a higher capability by the calling terminal than can be recognized by the called terminal, the called terminal may not be able to respond and establish an intelligible communication link. This turn of events leads to a loss of time in the user utilizing trial and error techniques until call establishment is acknowledged by the called terminal, if acknowledged at all.
In addition to the above-mentioned concerns with call initiations, other concerns exist for call modification. During a call, sometimes it is necessary to modify the nature of the connection or application that is using the connection, such as when a user changes a normal telephone call to a conference call in which the capacity of the channel being used must be expanded. This problem has been addressed in the ISDN environment, which implements signaling to tell when modification is necessary. Unfortunately, current PSTN modem equipment is unable to implement this capability.